Electrostatic type focussing device for hollow tubular electron beams



Jan. 21, 1964 w. HENNE ETAL & 3 ELECTROSTATIC TYPE FOCUSSING DEVICE'FORHOLLOW TUBULAR ELECTRON BEAMS Filed March 8, 1960l/l/I//l/l/I/l/I//l///////////////? ll///l//l//l/l//l/l//l//l/lI/I/fl//I INVENTORS t'l/l/l/ will i ba d Henne a I Rudolf John`e & fla

ATTORNEY United States Patett O 3,119,044 ELECTROSTATIC TYPE FOCUSSINGDEVICE FOR HOLLOW TUBULAR ELECTRON BEAMS Wiliibaid Henne and RudolfJohne, Ulm (Danube), Germany, assignors to TeiefunkenAktiengesellschaft, Berlin, Germany Filed Mar. 8, 1960, Ser. No. 13,581Claims priority, application Germany Mar. 12, 1959 3 Claims. (Ci.SIS-3.6)

The present invention relates to a focussing device of a tubularelectron beam in an electron ray tube, particularly tubes of thetravelling wave-tube type.

In general, it is often necessary to keep an electron beam constant withrespect to its cross-sectional dimensions and its thickness over adistance which is large as compared with the diameter of the beam if thelatter is of tubular shape. Such linear and straight propagatingelectron beans are used, for example, in travelling wave tubes in whichan electromagnetic wave propagates along a delay line and interacts withthe electron beam migrating adjacent thereto. Basically, two types offocussing devices for electron beams are known, one type Operating withthe aid of magnetic fields and the other type operating with the aid ofelectrostatic fields. The present invention pertans to focussing systemsOperating on the electrostatic principle.

It is known in the art to focus a tubular electron beam by means of twoelectrodes which are positioned inside and outside, respectively, of thetubular beam. The focussing electrodes are coaxial with the beam, andthey are connected to respective voltage potential sources. It isdesirable to use one of these electrodes as a delay line and waveconductor along which the electromagnetic wave travels, so as tointeract with the electron beam. For reasons of input and outputcoupling, only the outer focussing electrode can reasonably be used asdelay line or wave conductor.

It is, therefore, an object of the present invention to provide a newand improved focussing device for tubular electron beams which overcomethe deficiencies outlined above.

It is another object of the present invention to provide a new andimproved focussng system and device for a tubular electron beam withinner and outer focussing means in which the outer focussing means areof a uniform structure and serve as a single part for D.C. potentialdistribution as well as for high frequency conduction.

With the above objects in View, one aspect of the in- Vention, in apreferred embodiment thereof, comprises a first integral electrode,preferably in the form of a helical coil, which is positioned around thetubular electron beam and is connected to a D.C. voltage source so asotobe maintained at a constant and substantially uniform potential toproduce a radially directed electrostatic field. Inside of the electronbeam there is positioned an electrode assembly adapted to produce aradially directed electrostatic field which is constant as to time butvaries in axial direction according to a periodic function.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a cross-sectional View through a portion of an electron beamtube incorporating one embodiment of the present invention; electricalconnections as far as necessary are shown in schematical form.

FIGURE 2 is a cross-sectional View through a tube modified as comparedwith the one shown in FIGURE 1.

In FIGURE 1, a tubular enclosure 1 made, for example, of ceramic orglass, houses the various parts of an electron ray tube whose cathode orelectron gun, grid anode and target electrode, if any, are not shown,inasmuch as they are of conventional type and mounted inside of tube 1in a conventional manner.

The electron gun produces a tubular electron' beam 2. Inside of thespace enclosed by this tubular electron beam 2. are two helical coils 3and 4 which extends symmetrically with respect to the axis of theelectron beam 2, i.e., coaxially with the beam. Coils 3 and 4 aresimilar to a bifilar coil, but they are separated from each otherelectrically.

Outside of beam 2, in coaxial relationship thereto, is a single helicalcoil 5 positioned in close proximty to the beam. Coils 3 and 4 aremounted on ceramc or glass rods such as 6, while coil 5 is supported bysimilar rods such as '7. These supporting rods are conventional.

Coil 5 is connected to a voltage potential source 8 producing a voltagewhich preferably is positive relative to the potential of the electronbeam, i.e., positive relative to the electron gun producng the beam. Thevoltage potential source should have a Very low ohmic resistance so thata current produced by stray electrons which strike the electrode S andflow to ground via the voltage potential source will not change theuniform potential all along coil 5. Thus, a uniform radially-directedfield is produced which compensates for the outwardly directed spacecharge of the tubular beam.

Coils 3 and 4 are connected to D.C. voltage sources 10 and 11,respectively. The voltages applied to coils 3 and 4 preferably arepositive with respect to the potential of the electron gun producing theelectron beam 2 and they are selected or adjusted dilferently. As aresult, there is produced inside of the tubular beam, a spatiallystationary but axially periodically Variable electric field whichcompensates for the inwardly directed space charge of the tubular beam.

The entire device as described thus far serves as a focussing means forthe tubular electron beam. In addi ton, the outwardly positionedfocussing electrode, i.e., the coil 5 can serve also as a delay andtransmission line for electromagnetic waves, so that no difliculties areencountered as far as coupling and damping are concerned. This isparticularly important because in this case the wave propagation Will becarried out along a unifilar coil.

FIGURE 2 illustrates a modification of the structure shown in FIGURE 1.The outer focussing electrode is also the coil 5 but the innerelectrodes are formed by a plurality of rings 14, 14', 14", etc., whichalternate with rings 15, 15', 15", etc. All rings are similar in sizeand dimension, but rings 14, 14', 14", etc., are connected via a common,low ohmic conductor 1461 to a voltage source 10'. Rings 15, 15', 15" areelectrically interconnected by a low ohmic conductor lsa to a voltagesource 11'. Rings 14, 14', 14" are maintained at a potential which isdifferent from the potential of the rings 15, 15', 15". Thus, the ringscooperate with each other to produce an axially periodic and symmetricelectric field which does not vary in time.

lt will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. A combined transmission line and focussing device for a tubularelectron beam, comprising: a two-threaded electrode coil positionedinside of the electron beam and arranged coaxially therewith; means forapplying two different constant voltage potentials to the two threads ofsaid electrode coil; a unifilar coil positioned outside of said beam andarranged coaxially therewith, said coil constituting a transmisson linefor electromagnetic waves;

3 and means for applyng a constant voltage to said unifilar coil.

2. A combined transmisson line and focussing device for an electronbeam, comprising: a unifilar coil surrounding the beam and constitutinga transmission line therefor, means for maintaining said col at aconstant potential for producing a substantially radially directedconstant electrc field, a piurality of first eiectrode rings coaxiallypostioned inside of said beam, a plurality of second electrode ringscoax'ally positoned inside of said beam in alternating 'elatonship tosaid plurality of first rngs; first conductive means for electricallyinterconnecting said first plurality of electrode rings; secondconductive means separate from said first conductive means forelectrically interconnecting said plurality of second electrode rings;and means for applying dissmilar constant voltage potentials to saidfirst rings and said second rings, respectively.

3. A combined transmission line and focussing device as defined in claim2 wherein said rings are of the same size dimension.

References Cited in the file of this patent UNITED STATES PATENTS2,823,333 Quate Feb. 11, 1958 2,843,776 Tien July 15, 1958 2,843,792Pierce July 15, 1958 2,887,609 Dodds May 19, 1959

1. A COMBINED TRANSMISSION LINE AND FOCUSSING DEVICE FOR A TUBULARELECTRON BEAM, COMPRISING: A TWO-THREADED ELECTRODE COIL POSITIONEDINSIDE OF THE ELECTRON BEAM AND ARRANGED COAXIALLY THEREWITH; MEANS FORAPPLYING TWO DIFFERENT CONSTANT VOLTAGE POTENTIALS TO THE TWO THREADS OFSAID ELECTRODE COIL; A UNIFILAR COIL POSITIONED OUTSIDE OF SAID BEAM ANDARRANGED COAXIALLY THEREWITH, SAID COIL CONSTITUTING A TRANSMISSION LINEFOR ELECTROMAGNETIC WAVES; AND MEANS FOR APPLYING A CONSTANT VOLTAGE TOSAID UNIFILAR COIL.